largefiles: don't print files as both large and normal in addremove dryruns

largefiles: return the list of added files from addlargefiles() This will be used to exclude largefile candidates from the normal file matcher, which will allow add and addremove dryruns to not print a file as both a normal and a large file.

largefiles: align the output messages for an added file with core methods Core addremove prints the file relative to cwd only if patterns are provided to the command. Core add always prints relative to cwd. Also, both methods print the subrepo prefix when needed. The 'already a largefile' doesn't have an analog in core, but follows the same rules for consistency.

largefiles: align the output messages for a removed file with core methods Both cmdutil.remove() and scmutil.addremove() require verbose mode or an inexact match to print the filename. Core addremove also prints the file relative to cwd only if patterns are provided to the command. And finally, both methods print the subrepo prefix when needed.

revset: use '%' as an operator for 'only' With this patch, we can make it much easier to specify 'only(A,B)' -> A%B. Similarly, 'only(A)' -> A%. On Windows, '%' is a semi-reserved symbol in the following way: using non-bash shells (e.g. cmd.exe but NOT PowerShell, ConEmu, and cmder), %var% is only expanded when 'var' exists and is surrounded by '%'. That only leaves batch scripts which could prove to be problematic. I posit that this isn't a big issue because any developer of batch scripts already knows that to use '%' one needs to escape it by using a double '%%'. Alternatives to '%' could be '=' but that might be limiting our future if we ever decide to use temporary assignments in a revset.

transaction: support for callbacks during abort Previous transaction work added callbacks to be called during regular transaction commit/close. As part of refactoring Mozilla's pushlog extension (an extension that opens a SQLite database and tries to tie its transaction semantics to Mercurial's transaction), I discovered that the new transaction APIs were insufficient to avoid monkeypatching transaction instance internals. Adding a callback that is called during transaction abort removes the necessity for monkeypatching and completes the API.

debugnamecomplete: use new name api Instead of hardcoding a list of places to check, we use the new repo.names api to get a list of potential names to complete.